The present invention relates to a machine for manufacturing from chopped cellulose chips thin shavings or flakes which are cut substantially in the direction of the fibres and which have a relatively large surface in relation to thickness.
Shavings of the aforementioned kind can be used for the manufacture of particle board and as raw-material in different pulping processes, including chemical, mechanical and thermal processes, and combinations thereof.
The conventional method of producing pulp directly from chips is encumbered with a number of serious disadvantages. These disadvantages are particularly manifest when using wood originating from sub-tropical and tropical climates, since such raw-material often comprises wood of different hardness. Because of the varying hardness of such wood, digestion and impregnation of the wood in pulping processes is uneven, which results in an uneven and varying yield. Because of the relatively large thickness of the chips, normally from 3-6 mm, the time for the impregnating liquid to penetrate the chips and to diffuse therethrough varies greatly with both chip thickness and chip density.
For the purpose of eliminating these disadvantages, it has been proposed to use shavings or flakes, which are thinner and of more uniform thickness than conventional chips. It has been discovered that thin and uniform shavings drastically shorten both impregnating times and digestion times, beside reducing the chemical consumption and heat requirement during a pulping process.
These results are very favorable, since they save energy, reduce investment costs for new pulping plants, and reduce the emission of deleterious substances to the environment. At present, technologies for the manufacture of pulp by using shavings and steam-phase digestion techniques in extremely high wood/liquid ratios are being developed in many places. By using these methods, investment costs can be reduced to as low as about 25% of those costs incurred when using present day technology in comparable plants.
The desired reduction in the thickness of chips for creating advantageous process conditions requires, however, the chips to be sliced in the plane of the fibres, suitably in the longitudinal direction, so that the average fibre length is not shortened to any appreciable extent. This requires the chips to be oriented in a specific direction prior to being cut.
Present day machines for slicing chips into thin shavings do not operate satisfactorily, however, and hence cannot be used on an industrial scale. In certain kinds of such machines the cutting pressure exerted on the chips against the knive means is not sufficiently great, thereby lowering the capacity of said machines to an unsatisfactory level. In other machines of the said kind, the means for feeding the chips and shavings, respectively, are inefficient, resulting in blockages.
Other methods of producing high-quality shavings are known, in which the shavings are cut directly from logs or blocks, thereby avoiding the intermediate chip-producing stage. These methods, however, are encumbered with a number of serious disadvantages, since they require a high-quality rawmaterial. Further, the knife means rapidly become blunt when cutting thin shavings directly from logs or blocks of hardwood. On the other hand when producing shavings or flakes from wood-chips, the chips can readily be softened with steam prior to being cut. This procedure, however, is practically impossible when the raw-material comprises large logs or blocks.
The main object of the present invention is to provide a machine in which the aforementioned disadvantages are eliminated and which enables cellulose chips to be reduced to the form of thin shavings or flakes in a simple and effective manner.